Scandium(III) solvation and association and water structure in the gigapascal pressure range investigated by neutron scattering

Yamaguchi, Toshio*; Machida, Shinichi*; Hattori, Takanori   

1 (mol/kg) ScCl aqueous solution in DO was investigated under the thermodynamic conditions from 0.1 MPa/298 K to 4 GPa/523 K by in-situ neutron diffraction coupled with the empirical potential structure refinement (EPSR) method. A predominant Sc(III) species is [Sc(OH)] with a distorted pentagonal bipyramidal geometry together with appreciable amounts of contact ion pair species [ScCl(OH)] (n=1-3) and [Sc(OH)] with mean Sc-Cl and Sc-OH distances of 2.42 and 2.11O distance of 3.10 at 0.1 MPa/298 K and 4 GPa/523 K, respectively. Applying GPa pressure transforms the tetrahedral network structure of water under ambient conditions to a dense, randomly packed structure with a mean coordination number of 12.6, resulting in an increase in the first-neighbor distance from 2.77 to 2.89 AA. The hydrogen bonds between water molecules remain linear but are largely distorted at high temperatures and high pressures.